Activity Report 1995 - 1999
prepared by
H. Sünkel


The International Geoid Commission (IGeC) was formed by the International Association of Geodesy (IAG) at the XIXth General Assembly of the International Union of Geodesy and Geophysics in Vancouver, 1987. It operates as Commission XII of Section III of IAG. The presidents and secretaries of IGeC since 1987 were
Period President Secretary Secretary
1987 - 1991 R.H. Rapp A.H.W. Kearsley C.C. Tscherning
1991 - 1995 H. Sünkel A.H.W. Kearsley C.C. Tscherning
1995 - 1999 H. Sünkel A.H.W. Kearsley D.G. Milbert

An Executive Committee was established to support the Commission in forming directions. For the time being 44 countries are represented in IGeC.

In the sequel the main activities of the Geoid Commission in general and of geoid related activities in particular are reported.

The International Geoid Service (IGeS)

The International Geoid Service (IGeS) was established at the Politecnico di Milano and became operative on September 1, 1992. IGeS is supported by the Consiglio Nazionale delle Ricerche of Italy, the Dipartimento del Territorio, the Istituto Geografico Militare Italiano, the Istituto Nazionale di Geofisica of Italy, the Telespazio S.p.A., and by Politecnico di Milano. IGeS is presided by F. Sansň and has four staff members.

IGeS has been designed as the working arm of IGeC. In particular, IGeS works as a nonprofit organization for the benefit of the international geoscientific community. Its main duties and goals are as follows:
Collection of data related to geoid determinations that are not already systematically collected by other agencies or services, making sure that all data sets provided to IGeS are properly documented.
Collection of available software for geoid determinations, giving room to the wide pluralism of methodologies, and verifying that the software is properly documented and complete with test examples.
Collection and testing of global geopotential models and the corresponding software to produce various functionals of the geopotential at prescribed locations.
Collection and documentation of preprocessing software, including the first statistical tests on data, rejection of outliers, and data gridding.
Computation of geoids in exceptional cases, as defined by the Executive Committee (EC) of the IGeC, in support of national and scientific objectives.
Pursuing both theoretical and practical work towards the merging of regional geoids into larger solutions.
Dissemination of available geoid-related documented data sets and software upon request.
Organization of courses on special demand for users who would like to acquire the necessary knowledge to perform geoid computations on their own.
Participation in outstanding international research projects related to geoid determination such as ESA's gravity gradiometry mission GOCE.
Establishment of a close cooperation with the Bureau Gravimetrique International (BGI), starting with a pilot project aiming at the collection and homogeneization of digital elevation models for Europe for the purpose of geoscientific applications.
Preparation and distribution of a bi-annual bulletin describing the current activities and the information available at IGeS.
Pursuing any other task that the EC of the IGeC would assign to it.
Since its foundation IGeS has issued 9 IGeS Bulletins.

Foundation of Sub-Commissions

During the reporting period the following sub-commissions of IGeC were formed:
Year Region
1995 South-East Asia
1996 South America
1997 North America
3. Scientific Meetings and Schools

During the reporting period 1995 - 1999 the following scientific meetings and schools related to geoid determination were organized:
International Summer School of Theoretical Geodesy, Como, May 27 - June 7, 1996
International Symposium on Gravity, Geoid, and Marine Geodesy, Tokyo, September 30 - October 5, 1996
Second International School for the Determination and Use of the Geoid, Rio de Janeiro, September 10 - 16, 1997
Second Continental Workshop on the Geoid in Europe, Budapest, March 10 - 14, 1998
Second Canadian Geoid Workshop, Ottawa, May 14 - 15, 1998
Second Joint Meeting of the International Gravity Commission and the International Geoid Commission, Trieste, September 7 - 12, 1998
Third International School on the Determination and Use of the Geoid, Milan, February 15 - 19, 1999
National geoid activities

Apart from the mammoth task of the development of the Earth Gravity Field Model EGM96 by NASA, NIMA, and OSU and the geoid determination for Europe, which was pursued by the Hannover group with W. Torge and H. Denker, a huge number of geoid related activities went on worldwide.

From available progress reports and the submitted national reports the following information can be extracted:
The strongly growing GPS application community has a strong demand for an accurate and detailed geoid. Many countries have responded to this demand by providing a national geoid with a resolution of the order of a few kilometers.
Local and regional geoid determination has become feasible in numerous well observed areas with a relative accuracy of fractions of 10-6 with a resolution of a few kilometers half wavelength.
Geoid heights derived by GPS + orthometric heights are used extensively both to control national geoid solutions and to get hold on long wavelength errors which are mainly due to the shortcoming of the used global models.
GPS/levelling derived geoid heights are furthermore used as geoid observations for geoid determination purposes.
Altimeter derived sea surface heights combined with gravity data are used both for geoid determination in maritime countries and to separate the geoid from the sea surface topography.
Very high resolution digital terrain models (100 m or less) are becoming available in various countries, and are being used extensively for data reduction purposes.
The remove-restore technique (in various modifications) has become a standard procedure in context with gravity field determination in general and geoid determination in particular.
Spectral domain techniques such as FFT, the Hartley transform and the 1-D FFT technique proved to be extremely powerful and have become widely used by the international geodetic community for geoid determination purposes in many countries.
The EGM96 solution has proved to be a very significant leap forward in gravity field research and is being used by many organizations very successfully in context with geoid determination.
The geoscientific community is anxiously waiting for the realization of the three dedicated gravity field missions CHAMP (2000), GRACE (2001), and GOCE (2004). A successful completion of the missions presumed, the static gravity field, represented by the geoid, will become available with a resolution of the order of 80 km half wavelength and an accuracy of the order of 1 - 2 cm on a global scale. In addition, the temporal variations of the gravity field in the low to medium frequency range will be detected. These missions represent a quantum leap in gravity field research and will have an enormous impact on geoscientific research in general and on geodesy, oceanography, and solid Earth physics in particular.

Graz, July 1999 H. Sünkel